make_zip_contents_world_readable.py

#!/usr/bin/env python

import argparse
import logging
import os
import zipfile

logger = logging.getLogger(__name__)

def main(): # type: () -> None
    logging.basicConfig(level=logging.DEBUG)

    parser = argparse.ArgumentParser()
    parser.add_argument("zipfile")
    args = parser.parse_args()

    src = args.zipfile
    dst = args.zipfile + ".new"
    if os.path.exists(dst):
        raise Exception("Destination file (%r) already exists" % (dst,))

    logger.debug("Reading %r", src)
    with zipfile.ZipFile(src, 'r') as zf_src, zipfile.ZipFile(dst, 'w') as zf_dst:
        for info in zf_src.infolist():
            info_data = zf_src.read(info.filename)

            logger.debug("chmod a+r %r", info.filename)
            # From https://unix.stackexchange.com/questions/14705/the-zip-formats-external-file-attribute/14727#14727
            # TTTTsstrwxrwxrwx0000000000ADVSHR
            # ^^^^____________________________ file type as explained above
            #     ^^^_________________________ setuid, setgid, sticky
            #        ^^^^^^^^^________________ permissions
            #                 ^^^^^^^^________ This is the "lower-middle byte" your post mentions
            #                         ^^^^^^^^ DOS attribute bits
            info.external_attr |= 0444 << 16

            zf_dst.writestr(info, info_data)

if __name__ == '__main__':
    main()